Five per cent of watches made at a certain factory are defective.

sensational

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Five per cent of watches made at a certain factory are defective. Watches are sold to retailers in boxes of 40.

The question is:A big store bought 25 boxes of watches. Show that the probability that more than 70 watches are defective in those 25 boxes is 0.0015.

All I know in this question is to prove my answer to 0.0015 using the normal distribution. The number of watches=25*40=1000. µ=1000*0.05=5 one thing that I was unable to find is the standard deviation(σ)? Would anyone help find it or help find another way to solve the problem. If you have any idea please post cause Im stuck.
 
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Five per cent of watches made at a certain factory are defective. Watches are sold to retailers in boxes of 40.

The question is:A big store bought 25 boxes of watches. Show that the probability that more than 70 watches are defective in those 25 boxes is 0.0015.

All I know in this question is to prove my answer to 0.0015 using the normal distribution. The number of watches=25*40=1000. µ=1000*0.05=5 one thing that I was unable to find is the standard deviation(σ)? Would anyone help find it or help find another way to solve the problem. If you have any idea please post cause Im stuck.
You are correct that the expected number of defective watches would be (about) 50 [I assume the 5 instead of 50 was just a typo]. As far as finding the standard deviation, I don't think you have enough information given here to find it. Without the standard deviation (or an estimate of it) you can't do the problem.
 
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